In a packet transmitting/receiving circuit, the packet includes divided data and header information attached to the divided data. The header information includes information needed until the packet reaches a destination such as the destination information of the packet, a sequence number and a header error check code. The error check code is added to allow detection of whether an error has occurred in the packet or not. When the packet is received, the receiving circuit judges whether an error check code generated from the data coincides with the error check code added to the data or not. The receiving circuit detects whether an error has occurred in the packet or not.
Here, in a case that an error is found in the packet, the receiving circuit requests the transmitting circuit to re-transmit the packet. In a case that the packet is to be re-transmitted, information on up to which packet the receiving circuit has normally received and on which packet is requested to be re-transmitted to the transmitting circuit is needed. The transmitting/receiving circuit uses sequence numbers as the information concerned. The sequence numbers are added to the respective packets in order to confirm the order of the packet concerned and presence or absence of a missing packet. Control is performed such that the sequence number of the packet transmitted from the transmitting circuit matches the sequence number of the packet received by the receiving circuit. The transmitting circuit has a transmission counter for counting the sequence number and likewise the receiving circuit has a reception counter for counting the sequence number. When the packet transmitted from the transmitting circuit is normally received, the receiving circuit increments the reception counter. The receiving circuit transmits a signal indicative of normal reception of the packet to the transmitting circuit. The transmitting circuit receives this signal. Then the transmitting circuit increments the transmission counter. Upon transmission of the packet from the transmitting circuit, the value of the transmission counter coincides with the value of the reception counter.
In order to realize confirmation of transmission/reception of the packet concerned and controlling of packet re-transmission, the error check codes and the sequence numbers are needed. However, the sequence number has been added to the header information as redundant information, in spite of the fact that each of the transmitting circuit and the receiving circuit respectively manages the sequence number of the packet to be transmitted and the sequence number of the packet to be received.
Japanese Laid-open Patent Publication No. 2002-026963 has been proposed.